Parallel arcjet starter system

Abstract

There is disclosed an arcjet starter for igniting and sustaining an electric arc in an arcjet thruster. The arcjet starter is capable of delivering a short duration, high voltage pulse for igniting the arc and then providing a continuous low voltage, high amperage current for sustaining the arc. The starter has two separate magnetics, one for initiating breakdown in the arcjet and another for sustaining breakdown during steady state operation.

We claim: 
     
       1. An arcjet starter, the arcjet having a breakdown voltage, an initial voltage, and an operating voltage, comprising: a current supply;   a shunt circuit connected to the current supply and ground for establishing an initial current in the current supply;   a starter circuit connected between the arcjet and ground for initiating breakdown in the arcjet; and   a diverter switch connected between the current supply and the arcjet for connecting the current supply to the arcjet when the arcjet is in breakdown;   a control circuit for controlling the shunt circuit, the starter circuit, and the diverter switch.   
     
     
       2. The apparatus according to claim 1, wherein the diverter switch comprises at least one diode, the at least one diode having an anode and a cathode, the anode connected to the arcjet and the cathode connected to the current supply. 
     
     
       3. The apparatus according to claim 2, wherein the diverter switch further includes a single pole switch connected in parallel to the at least one diode for shunting the at least one diode when the arcjet is in breakdown. 
     
     
       4. The apparatus of according to claim 3, wherein the single pole switch is a vacuum relay. 
     
     
       5. The apparatus according to claim 1, wherein the shunt circuit comprises: at least one zener diode, having an anode, a cathode, and a clamp voltage having a magnitude higher than the initial magnitude of the arcjet voltage, connected between the current supply and ground, the anode connected closer to the current supply than the cathode; and   a shunt switch connected in series with the at least one zener diode for allowing current to flow from ground to establish the initial current in the current supply and for preventing current from flowing from ground through the shunt path after the arcjet voltage magnitude increases to a value higher than the clamp voltage magnitude.   
     
     
       6. The apparatus according to claim 5, wherein the shunt switch comprises: a single pole switch connected in series with the zener diode for connecting the zener diode to ground to establish current in the current filter and disconnecting the diode from ground after the arcjet voltage magnitude rises above the zener clamp voltage magnitude; and   a diode connected in series with the zener diode and the single pole switch, the anode connected closer to ground than the cathode.   
     
     
       7. The apparatus according to claim 6, wherein the single pole switch is a MOSFET. 
     
     
       8. The apparatus according to claim 2, wherein the shunt circuit comprises: a voltage source; and   a switch,   the voltage source and the switch connected in series, the switch allowing current to flow from ground to establish the initial current in the current supply and for preventing current from flowing from ground through the shunt circuit after the arcjet voltage magnitude rises above the zener diode clamp voltage magnitude.   
     
     
       9. The apparatus according to claim 1, wherein the starter circuit comprises: at least one diode, having an anode and a cathode, connected between the arcjet and ground, the anode connected closer to the arcjet than the cathode;   a transformer, having a primary winding and a secondary winding, connected in series with the diode, the primary winding coupled to a voltage source on a positive side and ground on a negative side, the secondary winding magnetically coupled with reverse polarity to the primary winding and connected in series with the diode to ground;   a switch connected in series with the primary winding to ground for connecting the primary winding to ground to initiate arcjet breakdown and disconnecting the primary winding after breakdown.   
     
     
       10. The apparatus of claim 3, wherein the reverse-bias clamp voltage of the zener diode is in the inclusive range 30 to 120 volts. 
     
     
       11. The apparatus of claim 9, wherein breakdown is initiated at approximately in the inclusive range of -1000 to -4000 volts. 
     
     
       12. The apparatus of claim 9, wherein the switch is a MOSFET. 
     
     
       13. A method for operating an arcjet comprising the steps of: establishing an initial current in a current supply path;   establishing a voltage on the arcjet sufficient to initiate breakdown; and   connecting the arcjet to the supply path after breakdown.   
     
     
       14. A method of operating an arcjet comprising the steps of: providing a current supply;   establishing an initial current in the current supply by connecting a shunt circuit to ground;   creating, after establishing the initial current, a voltage on the arcjet sufficient to initiate breakdown by connecting a starter circuit to ground;   connecting the arcjet to the current supply after breakdown; and   disconnecting the shunt circuit and the starter circuit from ground after breakdown.